Diseased heart valves often malfunction and this may eventually lead to heart failure and death. It is estimated that between 275,000 and 370,000 valve replacements are being performed each year.
The majority of these are done in the USA, Europe and Japan where access to cardiac surgery is widely available. In the developing world, patients often have no access to open heart surgery due to the absence of a heart lung machine. A procedure that does not require a heart lung machine, whilst being beneficial for certain groups in the developed world, is essentially the only option for the millions in the developing world.
Catheter-based endovascular procedures have been developed in which a catheter is inserted through a peripheral blood vessel or closed chambers of the heart. The method of choice for both the dilatation of stenotic valves and the expansion of crimped stent-mounted valves is balloon inflation. However, although ballooning of mitral valves has become a routine procedure over the past two decades, balloon obstruction of the aortic valve creates a very different situation. The obstruction of an inflow valve such as the mitral valve during the contraction of the heart (systole) does not limit the ability of the heart muscle to eject the blood, but obstruction of the aortic valve prevents the left heart chamber from emptying its contents. This isometric contraction leads to the generation of supra-systolic pressures which not only bear a high risk of valve dislodgement but also lead to overstraining of the heart muscle.
In order to overcome the dangers and complications associated with outflow obstruction during the balloon inflation, highly sophisticated approaches have been developed. To significantly reduce cardiac ejection during the procedure, rapid right ventricular pacing may be performed prior to inflation. The balloon then needs to be immediately inflated, deflated and withdrawn from the outflow tract.
Two or three balloon inflations are normally performed for effective predilatation of the replacement valve. Using the calcification of the native valve and a reference image obtained during supra-aortic angiography as markers, as well as sophisticated intra- and extra cardiac sonography, the centre of the catheter-mounted replacement valve may be accurately positioned in the middle of the native valve. Immediately prior to delivery, rapid pacing is again induced and the balloon is instantly inflated with contrast medium. After complete expansion, the balloon must be immediately deflated and the rapid pacing interrupted. The total duration of rapid pacing and balloon inflation should not exceed a few seconds.
Given the obstructive nature of expansion balloons, self-expanding valve stents made of shape memory alloys have been introduced. As their clinical success remains to be proven, pre-dilatation of the stenotic valve still requires a balloon. A variety of self-expanding valves has been reported ranging from the utilization of shape memory materials such as Nitinol to inflatable valve stents (U.S. Pat. Nos. 5,554,185; 4,655,771; 5,332,402; 5,397,351; 5,855,601; and 5,957,949 describe such valve stents.
Generally, deployment and/or dilatation devices share the problem of flow-occlusion during expansion. One proposed solution to maintain blood flow is based on rigid tubular structures providing a communication between the up-stream and down-stream lumen. (U.S. Pat. Nos. 4,661,094 and 4,790,315).
U.S. Pat. No. 5,158,540 discloses a motorized pump in a double-balloon design to increase the perfusion flow. U.S. Pat. No. 5,370,617 additionally discloses the use of the guide wire lumen after withdrawal of the guide wire to add luminal perfusion capacity.
Alternatively, the balloon component of dilatation/deployment catheters or devices can be replaced by a mechanical dilatation mechanism. In consequence, device expansion is not associated with obstructive occlusion of blood flow. However, this arrangement is not suitable for use with heart valve replacements as flow is permitted in both directions and thus the heart will not be able to pump blood during deployment.
Recognizing the importance of a balloon-based expansion system for both stenotic valvular lesions and non self-expanding stents, various inventions have dealt with overcoming blood flow obstruction. U.S. Pat. No. 6,458,153 discloses channels or ridges at the outside of the balloons to permit blood flow.
U.S. Pat. No. 6,007,517 describes an angioplasty balloon for coronary interventions with one or more asymmetrically positioned longitudinal channels aiming at the maintenance of blood flow through the expanded balloon.
Goldberger (U.S. Pat. No. 4,909,252) describes a donut-shaped balloon with a double-walled bladder, providing a central orifice. The invention is claimed for valvuloplasty but not stented valve expansion against calcific stenosis, as deliverable pressures may be insufficient.
Due to the scantiness of delivery systems making provision for sufficient blood-flow during the inflation of an expansion balloon, the issue of a need for biased flow direction has hardly been addressed heretofore.
Vesely (U.S. Pat. No. 6,530,952) describes a delivery system for an endovascular valve placement and replacement system that includes a ‘surgical platform’ anchoring the numerous catheters and devices in space, thereby ensuring proper controlled manipulation. An integrated check valve within this surgical platform would enable controlled ejection of blood from the ventricle during valve placement or removal. Its location distal from the replacement valve brings the coronary ostia onto the wrong side of the check valve, preventing blood filling of the coronary arteries from the aorta during diastole. Similar shortcomings can be ascribed to the Medtronic invention of a temporary heart valve in the ascending aorta (Allen US patent application 2004/0225354). A similar principle underlies the Lashinski patent application (US 2006/0020332).